Reverse flow cooling system for a dynamoelectric machine

ABSTRACT

A dynamoelectric machine with internal gas cooling system has a reverse flow pattern with gas flowing from the fan through the coolers and then to the parts to be cooled. The gas is separated into two flow portions at the cooler, one portion undergoing a low pressure drop and then serving to cool the rotor end turns and transition section, the other undergoing a relatively high pressure drop and then serving to cool the stator core and to supply the gas gap for &#39;&#39;&#39;&#39;gap pickup&#39;&#39;&#39;&#39; cooling of the rotor body.

limited States Patent 1191 Shartrand REVERSE FLOW COOLING SYSTEM FOR ADYNAMOELECTRIC MACHINE Allan c. Shartrand, Scotia, NQY.

General Electric Company, Schenectady, NY.

Filed: Dec. 3, 1971 Appl. No.: 204,582

Inventor:

Assignee:

[52] US. Cl. .l 310/58 Int. Cl. 1102k 9/00 [56] References CitedUNITED'STATES PATENTS 1 l/1963 Baudry 310/55 11/1954 Kilbourne 310/649/1966 Philofsky ..310/55 5/1963 Shartrand ..3l0/55 Field of Search31-0/52, 58, 55-57,

11 3,739,208 June 12, 1973 3,348,081 10/1967 Willyoung 310/55 3,005,11510/1961 Adamsheck 307/156 2,986,664 5/1961 Willyoung 310/61 1,672,6806/1928 Freiburghouse 310/57 Primary Examiner-R. Skudy Attorney-WilliamC. Crutcher and James W. Mitchell [57] ABSTRACT A dynamoelectric machinewith internal gas cooling system has a reverse flow pattern with gasflowing from the fan through the coolers and then to the parts to becooled. The gas is separated into two flow portions at the cooler, oneportion undergoing a low pressure drop 7 and then serving to cool therotor end turns and transition section, the other undergoing arelatively high pressure drop and then serving to cool the stator coreand to supply the gas gap for gap pickup cooling of the rotor body.

8 Claims, 1 Drawing Figure oucoo 00000 0000019 BACKGROUND OF THEINVENTION This invention relates to large gas-cooled dynamoelectricmachines with internal cooling systems, and more generally relates tolarge generators with radial flow cooling of the stator core andemploying the gap pickup method of cooling the rotor.

As the ratings of large dynamoelectric machines such asturbine-generators on the order of 800 MW or more have developed, it hasbecome increasingly difficult to obtain proper cooling of the rotor andstator windings and other parts of the machine. Systems have beendeveloped for flowing liquid and gaseous coolants inside the windingconductors, as disclosed in U.S. Pat. No. 2,695,368 to C. E. Kilbourne.Effective methods for cooling the rotor windings by coolant picked upfrom the gas gap by pumping action of the rotor are disclosed in U.S.Pat. No. 3,348,081 to D. M. Willyoung.

One of the more difficult portions of the rotor winding to cool properlyis the rotor end turn region beneath the retaining ring holding thewindings in place and the transition section in the end part of the bodyportion of the rotor. Although constructions have been suggested forimproving cooling of the end turn windings and transition section, theseare always dependent upon the pressure drop which is available to forcethe cooling gas to flow through the end turn and transition region.

A construction is disclosed in U.S. Pat. No. 1,672,680 to E. H.Freiburghouse in which the cooling gas in an aircooled generator flowsin a reverse direction from the conventional pattern, going to thecoolers before it flows to the machine parts to be cooled. In thatpatent, the gas flow divides into two paths, one path flowing to the airgap through the stator and the other portion flowing to the air gapthrough the rotor body. The aforesaid construction used air and did notcool the windings internally, but merely flowed air over the rotor bodyand stator core themselves. Much higher pressure heads could bedeveloped in air than in hydrogen, which is the most commonly usedgaseous coolant today.

Another arrangement in the prior art which requires high-pressuremultistage blowers to obtain the necessary pressure differentials forcooling with hydrogen gas is disclosed in U.S. Pat. No. 3,110,827 to R.A. Baudry. This patent shows a reverse flow of gas to the cooler, therotor end turn portion of the cooling gas undergoing a higher pressuredrop by passing through two sections of the cooler, while the statorportion of the cooling gas undergoes a lower pressure drop by passingthrough only one section of the cooler. The remainder of the rotorcoolant pressure head is necessary to force the gas through thepartitioned rotor winding cooling passages.

The aforesaid reverse flow constructions either use air as the coolant(which causes too much power loss due to windage) or requires ahigh-pressure blower. A construction would be desirable in which highpressure drops could be obtained across the rotor end turn andtransition cooling region in machines of the gap pickup" type dependingupon the pumping action of ;he rotor for the rotor cooling and usinglow-pressure .ans.

Accordingly, one object of the present invention is to provide animproved dynamoelectric machine cooling construction for enhancingcooling of the rotor end turns and transition section.

Another object of the invention is to provide an improved coolingarrangement in a generator of the type using gap pickup cooling andlow-pressure fans.

SUMMARY OF THE INVENTION DRAWING The subject matter which is regarded asthe invention is particularly pointed out and distinctly claimed in theconcluding portion of the specification. The invention, however, both asto organization and method of practice, together with further objectsand advantages thereof, may best be understood by reference to thefollowing description taken in connection with accompanying drawing, inwhich the single FIGURE is an elevation view, in section, of the tophalf of a dynamoelectric machine at one end thereof, the other end beingidentical.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, adynamoelectric machine has a gas-tight casing 1 containing hydrogencooling gas. A stator core 2 of laminations or punchings is constructedin conventional manner with the punchings arranged in packages of shortaxial length with radial cooling passages 3, 4 provided therebetween bymeans of suitably arranged spacers. Generator core 2 has slotscontaining a main armature winding 5 cooled by a separate liquid coolingsystem which is not material to the present invention.

Within the stator casing l is a rotor 6 having a body portion 7 spacedfrom the stator 2 by a gas gap 8. Rotor 6 also has an end turn portion 9at either end thereof which includes a retaining ring 10 holding the endturns III in place. A transition section 7a at the end of rotor body 7receives its cooling gas from the end of the rotor. The rotor carries aset of fan blades 12 into which gas is guided by stationary vanes 13.

The body portion 7 of the rotor is cooled by gas picked up from the gasgap 8 in the manner of the aforementioned Willyoung U.S. Pat. No.3,348,081. Gas is directed to an axially spaced section along the gasgap through internal diagonal cooling passages through the rotorwindings, a suitable construction being disclosed in U.S. Pat. No.2,986,664 to D. M. Willyoung and P. A. Becker which is assigned to thepresent assignee and incorporated herein by reference. There is nosubstantial pressure difference along the gas gap 8 between the inletand outlet zones.

The end turn region 9 is arranged with internal baffling and coolingpassages through the end windings 11 leading to an outlet 14 into thegas gap. A suitable arrangement for accomplishing this is disclosed inU.S.

- herein by reference.

Cooling of the transition section 7a is accomplished by gas inthe endturn region which passes through a subslot (not shown) to the gas gap 8,joining gas from outlet 14, as shown schematically by dotted arrow 7b.

Additional cooling of the end region 11 may be accomplished by means ofcentrifugal fan blades 15 disposed at the end of retaining ring andconnected by internal passages to the chamber beneath the retainingring. A suitable construction is disclosed in U.S. Pat. No. 3,225,231,assigned to the present assignee and incorporated herein by reference.

in accordance with the present invention, a dual cooler 16 is disposedin the casing l. The cooler is divided into two sections, one section 17providing a relatively low pressure drop as it cools the gas flowingtherethrough, and the other section 18 providing a relatively highpressure drop. This relative difference in pressure drops may beprovided by means well known to those skilled in the art, such as bymore densely packing the cooling tubes in section 18 than in section 17as schematically illustrated in the drawing, or by making section 18 oflonger length, or by providing suitable downstream and/or upstreamrestrictions for section 18. It should be apparent that the dual cooler16, though illustrated as a horizontal transverse cooler in thearrangement shown, could also be vertical or extend longitudinally, theparticular physical arrangement of the cooler sections not beingmaterial to the present invention. Sections 17 and 18, although shown aspart of a single cooler for convenience of connecting piping, could alsobe separated and placed in separate portions of the flow path.

A series of internal baffles and flow-guiding tubes serve to guide thegas in the desired flow paths. These are illustrated schematically inthe drawing, it being understood that in actual machines, the flow oftentakes circuitous paths through suitably arranged baffles and openings,the exact details of such an arrangement not being material to thepresent invention.

As illustrated herein, a first path is provided from the low-pressuresection 17 of the cooler through one or more tubes 19 to an end chamber20 formed between a casing end wall 21 and a flow-dividing wall 22.Openings 23 into the rotor shaft lead through internal longitudinalpassages 24 beneath fan 12 into the end turn region beneath retainingring 10. Part of this gas cools the transition region 7a (see flow arrow7b) and the other part cools the end turns leaving through opening 14.These two flows leave the gas gap, flowing past a flowrcstricting baffle25 and re-join the remainder of the gas from centrifugal blades at thesuction side of fan 12. The gas then flows through an end passage 26provided between walls 22 and 27 back to cooler 16.

The other main flow of gas from the high-pressure cooler section 18 isdistributed longitudinally along the stator by means of tubes such as28, 29 and is distributed into alternating circumferential inletchambers 30, 31 around stator core 2. Because of the great number ofparallel flow paths to the gas gap the pressure drop from cooler 18 tothe gas gap is relatively low. Alternating between the circumferentialinlet chambers 30, 31 are outlet chambers 32, 33'from which gas iscollected and moved longitudinally in tubes 34, 35 to the stator endturn region 36 and thence to the suction side of fan 12. From there itflows back to cooler 16.

OPERATION The operation of the invention can best be described byfollowing the two gas flow paths from one pressure region to the next.The letters A through G are used to designate successively lowerpressure regions relative to the head developed across fan 12. Fromregion A at the outlet of fan 12, the total gas flows to region B at theinlet to the cooler sections 17, 18. One part of the gas undergoes arelatively low pressure drop B-C through section 17 to a pressure regionC and then flows into end passage 20, through the rotor longitudinalpassage 24 into a pressure region D beneath the retaining ring. Thesepassages connecting region C to D constitute first conduit means.

With reference to the other portion of gas at the cooler, the gasflowing through section 18 undergoes a relatively large pressure dropB-E to a pressure region E and then flows into the peripheral chambers30, 31. Then it flows into pressure region F in the gas gap 8 throughthe radial cooling passages 3 undergoing a relatively low pressure dropE-F. These passages connecting region E to F constitute second conduitmeans. After the gas in the gap 8 has been scooped up to cool the rotorand returned to the gap, it flows from pressure region F radiallyoutward in passages 4 and is returned to the stator end region G whichis substantially at a pressure corresponding to the low-pressure side offan 12. These passages connecting region F to G via passages 4constitute third conduit means. A portion of the gas from the gap 8 alsoflows past the restricted baffle 25 to pressure region G. The passageconnecting region F to G via the baffle 25 constitutes fourth conduitmeans. Both of these pressure drops F-G are relatively low.

It will be observed that a large static pressure head D-F is availableto force gas from the space beneath the retaining ring to gas gap 8through opening 14, [and holes from transition section (not shown)] inaddition to any additional pumping head developed by the rotor itself.In addition, there is an even greater pressure head D-G available toforce gas through the end turn winding passages leading to thecentrifugal blades 15. These passages from region D to G via thecentrifugal blades 15 constitute fifth conduit means. The existence ofthis pressure head across the end turn windings and transition sectionat the end of the body, separate from the main body portion cooling ofthe rotor (accomplished only by the pumping action of the rotor) aids tomore effectively cool the end turn windings. The means by which thisadditional head is developed in the critical end turn and transitionregion is preferably by means of the dual cooler, by virtue of itsseparate section for cooling the gas flowing through the end turncooling circuit.

As will be apparent to those skilled in the art, a greater pressure dropin the cooling circuit feeding the stator core and air gap can also beaccomplished by introducing restrictions in or by properly sizing tubes28, 29 and it is intended to cover these modifications in the presentinvention. The restriction to induce higher pressure drop could also beincorporated into the stator core inlet ducts, 3, themselves. However,the preferred means of introducing differences in the gas pressure dropis within the cooler itself.

, scope of the invention.

What is claimed is: 1. In a dynamoelectric machine of the type having agas-tight casing filled with cooling gas, a stator core with radialcooling ducts, a rotor defining a gas gap with the stator core andhaving a body portion cooled by pumping action from the gas gap and anend turn portion, said rotor having fan means mounted thereon forcirculating the cooling gas, the improvement comprising:

first and second cooler sections disposed within said casingcommunicating directly with the outlet of said fan to cool the gastherefrom, said first cooler section being arranged and proportioned tocause a lower pressure drop of the gas flowing therethrough than saidsecond cooler section, first conduit means conducting gas from saidfirst cooler section to said rotor end turn portion,

second conduit means conducting gas from said second cooler section andthrough selected stator radial cooling ducts to the gas gap,

the flow path-through the first cooler section and the first conduitmeans being arranged and proportioned toprovide a lower gas pressuredrop than the flow path through the second cooler section and the secondconduit means, whereby a remaining pressure drop is available betweenthe end turn portion and the gas gap for forcing cooling gas through theend turn portion.

2. The combination according to claim 1, further including a baffie inthe gas gap and fourth conduit means providing a restricted flow pathfrom said gas gap past said baffie to the suction side of the fan means,whereby a still greater pressure drop is available between said end turnportion and the suction side of the fan means to force cooling gasthrough the end turn portion.

3. The combination according to. claim 1, further including thirdconduit means from the gas gap through other stator radial cooling ductsto the suction side of the fan means.

4. The combination according to claim 1, wherein the first coolersection has cooling tubes therein less densely packed than cooling tubesdisposed in said second cooling section.

5. The combination according to claim 1,wherein said first conduit meansincludes a longitudinal passage through the rotor beneath said fanmeans.

6. In a dynamoelectric machine of the type having a gas-tight casingfilled with cooling gas, the combination comprising:

a stator core defining spaced groups of alternating inlet and outletradial cooling ducts,

a rotor mounted within the casing and defining a gas gap with saidstator core, said rotor having a body portion arranged with means toscoop gas from the gap and return it at an axially spaced location,

said rotor further including end turn and transition portions definingfirst internal gas cooling passages through the rotor end turn andtransition portions communicating with the gas gap,

fan means mounted on said rotor,

first and second cooler sections disposed within said casing, said firstcooler section being arranged to provide a lower pressure drop for gasflowing therethrough than the second cooler section, 1

first conduit means defining a flow path with a re latively low pressuredrop from said first cooler section into the rotor, and

second conduit means defining a flow path with a relatively low pressuredrop from said second cooler section through the radial inlet statorcooling ducts to the gas gap, whereby an additional pressure drop isavailable to force gas through said first internal cooling passages tothe gas gap.

7. The combination according to claim 6, further including third conduitmeans providing a flow path from said gas gap through the outlet radialcooling ducts to the suction side of the fan means, and fifth conduitmeans including second internal cooling passages in the rotor body endportion through the end windings directly to the suction side of the fanmeans.

8. The combination according to claim 7, further including a baffle inthe gas gap and fourth conduit means providing a restricted flow pathfrom the gas gap past said baffle'to the suction side of the fan means.

1. In a dynamoelectric machine of the type having a gas-tight casingfilled with cooling gas, a stator core with radial cooling ducts, arotor defining a gas gap with the stator core and having a body portioncooled by pumping action from the gas gap and an end turn portion, saidrotor having fan means mounted thereon for circulating the cooling gas,the improvement comprising: first and second cooler sections disposedwithin said casing communicating directly with the outlet of said fan tocool the gas therefrom, said first cooler section being arranged andproportioned to cause a lower pressure drop of the gas flowingtherethrough than said second cooler section, first conduit meansconducting gas from said first cooler section to said rotor end turnportion, second conduit means conducting gas from said second coolersection and through selected stator radial cooling ducts to the gas gap,the flow path through the First cooler section and the first conduitmeans being arranged and proportioned to provide a lower gas pressuredrop than the flow path through the second cooler section and the secondconduit means, whereby a remaining pressure drop is available betweenthe end turn portion and the gas gap for forcing cooling gas through theend turn portion.
 2. The combination according to claim 1, furtherincluding a baffle in the gas gap and fourth conduit means providing arestricted flow path from said gas gap past said baffle to the suctionside of the fan means, whereby a still greater pressure drop isavailable between said end turn portion and the suction side of the fanmeans to force cooling gas through the end turn portion.
 3. Thecombination according to claim 1, further including third conduit meansfrom the gas gap through other stator radial cooling ducts to thesuction side of the fan means.
 4. The combination according to claim 1,wherein the first cooler section has cooling tubes therein less denselypacked than cooling tubes disposed in said second cooling section. 5.The combination according to claim 1, wherein said first conduit meansincludes a longitudinal passage through the rotor beneath said fanmeans.
 6. In a dynamoelectric machine of the type having a gas-tightcasing filled with cooling gas, the combination comprising: a statorcore defining spaced groups of alternating inlet and outlet radialcooling ducts, a rotor mounted within the casing and defining a gas gapwith said stator core, said rotor having a body portion arranged withmeans to scoop gas from the gap and return it at an axially spacedlocation, said rotor further including end turn and transition portionsdefining first internal gas cooling passages through the rotor end turnand transition portions communicating with the gas gap, fan meansmounted on said rotor, first and second cooler sections disposed withinsaid casing, said first cooler section being arranged to provide a lowerpressure drop for gas flowing therethrough than the second coolersection, first conduit means defining a flow path with a relatively lowpressure drop from said first cooler section into the rotor, and secondconduit means defining a flow path with a relatively low pressure dropfrom said second cooler section through the radial inlet stator coolingducts to the gas gap, whereby an additional pressure drop is availableto force gas through said first internal cooling passages to the gasgap.
 7. The combination according to claim 6, further including thirdconduit means providing a flow path from said gas gap through the outletradial cooling ducts to the suction side of the fan means, and fifthconduit means including second internal cooling passages in the rotorbody end portion through the end windings directly to the suction sideof the fan means.
 8. The combination according to claim 7, furtherincluding a baffle in the gas gap and fourth conduit means providing arestricted flow path from the gas gap past said baffle to the suctionside of the fan means.